1. Field of the Invention
The present invention relates to a magnetoresistive head (hereinafter, called MR head), and more particularly, to an MR head which is biased to a soft adjacent layer (hereinafter, called SAL) so as to make deflection angles at any point of the MR element uniform.
2. Description of the Related Art
An MR head basically consists of separate read and write elements. The write element is a thin-film inductive head and the read element consists of an alloy film, usually NiFe, that exhibits a change in resistance in the presence of a magnetic field, i.e., a magnetoresistive (MR) effect.
The MR head is known to have a superior capability of reading data from a magnetic recording medium to that of an inductive head or a thin-film head. The MR head detects a magnetic-field signal as a magnetic-flux function through a change in resistance of the read element made of a magnetoresistive material. Namely, as the resistance of the MR element varies according to the direction and size of the detected magnetic flux, the MR head is used to detect a magnetic signal from a magnetic recording medium.
FIGS. 1A through 1E are views for explaining a SAL-biased MR sensor according to the conventional technology. Here, FIG. 1A is a perspective view showing the structure of the MR sensor; FIG. 1B is a basic circuit diagram showing the MR sensor; FIG. 1C is a view showing the relationship between a SAL and the MR element; FIG. 1D is a view showing the direction and size of biasing at each point of the MR sensor; and FIG. 1E is a view showing a biasing angle at each point of the MR sensor.
Referring to FIGS. 1A and 1B, the MR sensor consists of a SAL 11 (15), a MR element 13 (16), and an insulator 12. Current i.sub.b and current i.sub.s respectively flow through the SAL 11 (15) and the MR element 12 (16) from a current source 14 (17).
Referring to FIGS. 1C, 1D and 1E, since the SAL 18 is formed in one body, the intensity of the magnetic field generated around the SAL 18 differs at each portion of the MR element 19. Also, it can be seen that the angle of deflection of an easy direction is not uniform in the MR element. That is, the sizes of H.sub.b at points A, B, C, D and E are different from one another so that the angle of deflection differs at every point. Due to this non-uniformity, noise is generated with the MR sensor and the MR ratio, .DELTA.R/R, that is an indicator of MR performance, deteriorates.
U.S. Pat. No. 3,864,751 to Beaulier et al., entitled Induced Bias Magnetoresistive Read Transducer, discloses a magnetoresistive (MR) read transduce that has one MR element an a soft magnetic bias film that is electrically insulated from the MR element. It is disclosed when current is applied to the MR element, the bias film is magnetically saturated, and provides a magnetizing bias field lo the MR element, wherein the bias field is independent of the sense current amplitude and of the output signal.
U.S. Pat. No. 4,833,560 to Doyle, entitled Self-Biased Magnetoresistive Reproduce Head, discloses a magnetoresistive reproduce head which is self-biased by a saturated soft adjacent layer magnetically coupled to the magnetoresistive element, wherein the induced anisotropy fields of the magnetoresistive element and the soft adjacent layer are made to lie in the direction of the bias field at the magnetoresistive element rather than perpendicular to the bias field. It is disclosed that these induced anisotropy fields partially counteract demagnetizing fields which oppose the bias field, and thereby lover the current in the magnetoresistive element required to saturate the soft adjacent layer in biasing the magnetoresistive element. It is disclosed the lowered current reduces the Joule heating of the magnetoresistive element.
U.S. Pat. No. 5,600,518 to Koga, entitled Magnetoresistive Head Having A Stepped Magnetoresistive Film Element, discloses a magnetoresistive head for use in, for example, a magnetic recording/reproducing device such as a magnetic disk unit. It is disclosed that the magnetoresistive head includes a substrate, a magnetoresistive element film, first and second antiferromagnetic films, and first and second lead layers mounted on the first and second antiferromagnetic films for supplying a sense current to the magnetoresistive element film. It is disclosed that the magnetoresistive element film includes first and second stepped side portions each having a thickness smaller than that of a central portion of the magnetoresistive element film which defines a reproducing section. The first and second antiferromagnetic films are disclosed as being formed on the first and second stepped side portions of the magnetoresistive element film. It is disclosed that Barkhausen noise is reduced while maintaining a reproduced output voltage at a desired level.
U.S. Pat. No. 5,694,275 to Watanabe et al., entitled Magnetoresistive Magnetic Head, discloses a magnetoresistive magnetic head having a laminate composed of a magnetoresistive (MR) layer showing the magnetoresistive effect, a SHUNT layer as a non-magnetic layer and a soft adjacent layer (SAL) for applying a transverse bias magnetic field to the MR layer, wherein the MR layer and the SAL are made of the same Ni.sub.81 Fe.sub.19 magnetic film. It is disclosed that since the SAL is magnetically saturated in the same direction as the direction of leakage flux of recording medium (y direction), permeability thereof in the y direction decreases, and the MR effect function therein can be restricted. It is disclosed that although the MR layer and the SAL have the same specific resistance, a sufficient detection current can be made to flow through the MR layer and a high-precision magnetic detection output can be obtained by making the MR layer thicker than the SAL.
U.S. Pat. No. 5,768,067 to Saito et al., entitled Magnetoresistive Head Using Exchange Anisotropic Magnetic Field With An Antiferromagnetic Layer, discloses a magnetoresistive head including a magnetoresistive film formed in a read-track region, and antiferromagnetic and ferromagnetic films are formed on each end of the magnetoresistive film outside of the read-track region such that bias magnetization is applied to the magnetoresistive film by exchange coupling between the antiferromagnetic film and the ferromagnetic film. It is disclosed a nonmagnetic intermediate film is formed between the ferromagnetic film and the magnetoresistive film for preventing ferromagnetic coupling on a contact boundary surface between the ferromagnetic film and the magnetoresistive film.
U.S. Pat. No. 5,805,389 to Saito et al., entitled Magnetoresistive Head, discloses a magnetoresistive head including longitudinal bias layers composed of .alpha.--Fe.sub.2 O.sub.3 provided under an magnetoresistive layer in close contact therewith, wherein an exchange anisotropic magnetic field is applied to the magnetoresistive layer from the longitudinal bias layers and the coercive force of the magnetoresistive layer is increased to several hundred Oe in exchange coupling regions with which the longitudinal bias layers are in close contact. It is disclosed the magnetization direction of the exchange coupling regions becomes stable in the x axis direction and sufficient longitudinal bias magnetic field is thereby applied to a region corresponding to the track width (Tw) of the magnetoresistive layer, wherein decreased Barkhausen noise and improved magnetic detection characteristics can be achieved.
"MAGNETORESISTIVE HEADS-FUNDAMENTALS AND APPLICATIONS", Academic Press, pages 25-27 and 76-77 (1996), discusses the anisotropic magnetoresistive effect, magnetoresistive sensors or elements, and shielded MRH designs. "THE ERA OF MAGNETORESISTIVE HEADS", IBM Storage, IBM Internet website, four (4) pages (Nov. 4, 1997) discusses MR head design and MR sensor technology, including a soft adjacent layer(SAL) biased-MR sensor structure, and giant magnetoresistive heads are discussed.